Editing Ratite (section)

===Loss of flight===

Loss of flight allows birds to eliminate the costs of maintaining various flight-enabling adaptations like high [[Bird anatomy#Muscular system|pectoral muscle]] mass, hollow bones and a light build, et cetera.<ref name = Mcnab1994 /> The basal metabolic rate of flighted species is much higher than that of flightless terrestrial birds.<ref name="Cubo"/> But energetic efficiency can only help explain the loss of flight when the benefits of flying are not critical to survival.

Research on flightless rails indicates the flightless condition evolved in the absence of predators.<ref name=Mcnab2006/> This shows flight to be generally necessary for survival and dispersal in birds.<ref name=Diamond1991/> In apparent contradiction to this, many landmasses occupied by ratites are also inhabited by predatory mammals.<ref name=Mitchell2014/> However, the [[K–Pg extinction event]] created a window of time with large predators absent that may have allowed the ancestors of extant flightless ratites to evolve flightlessness. They subsequently underwent selection for large size.<ref name=Phillips2010/> One hypothesis suggests that as predation pressure decreases on islands with low raptor species richness and no mammalian predators, the need for large, powerful flight muscles that make for a quick escape decreases. Moreover, raptor species tend to become generalist predators on islands with low species richness, as opposed to specializing in the predation of birds. An increase in leg size compensates for a reduction in wing length in insular birds that have not lost flight by providing a longer lever to increase force generated during the thrust that initiates takeoff.<ref name = Wright2016/>